Due to the increasing trend of photonic device miniaturisation, there is also an increased need for optical splitting in a small volume. We propose a smart solution to split light in three dimensions (3D). A 3D optical splitter based on multimode interference (MMI) for the wavelength of 1550 nm is here designed, simulated, fabricated and optimised for splitting at 1550 nm. We focus also on the possibility of its direct integration on an optical fibre. The design is focused on the use of 3D laser lithography based on the direct laser writing (DLW) process. The output characteristics are investigated by near-field measurement, where we confirm the successful 1 × 4 splitting on a 158 µm long MMI splitter.

Surface plasmon resonance (SPR)-based sensors have attracted huge interest due to their ability to provide real-time sensing of a wide range of quantities, while still boasting high sensitivity, low cost, and electromagnetic immunity. Among various types of these sensors, waveguide-based sensors show great promise in terms of integrability into more complex circuits while still maintaining similar sensitivity and versatility as their stand-alone counterparts. This paper presents the results of investigation based on design and simulation of optimal parameters for multimode SPR-based waveguide sensor sensitive to any commonly used liquid analytes. The sensitivity for a wider range of analytes is achieved by utilisation of SiON material platform because refractive index adjustability of SiON offers a way to tailor sensor’s sensitivity to exact applications and analytes. One of the research goals in this work was to show that multi-mode waveguides may be suitable for such sensors with comparable sensitivity and higher transmission rates as single-mode waveguides. To showcase design possibilities, two variations with the same design and material’s refractive index adjustment only were investigated, and their optimal parameters have been found. Sensitivity for all commonly used liquid analytes was validated, with sensitivity rising to 1400 nm/RIU for label-free refractive index sensing, even without the use of any sensitivity-enhancing structures.

Planar MMI couplers based on inorganic material platforms have played an essential role in photonic integrated circuits development. Advances in organic polymer fabrication techniques enable the design of components beyond a single plane, thus facilitating vertical integration for a wide range of components, including the MMI coupler. This paper presents the design of two 3D IP-dip polymer-based MMI power splitters operating in the near-infrared part of the spectrum at a wavelength of 1550 nm. The resulting output power ratio, modal field distributions, spectral characteristics, and the effects of input fibre misalignment are investigated using the beam propagation method. The fabrication method used to realise the designed splitters was direct laser writing. The function of the splitters was then verified by a highly resolved near-field scanning optical microscope.

Optical sensors play a crucial role in many fields today, and their use is becoming increasingly attractive. This is mainly due to their unique properties, which make them more technologically advanced than conventional electrical sensors. Sensors based on IP-Dip polymer in the form of a Fabry–Pérot interferometer (FPI), manufactured using direct laser writing (DLW) lithography and placed on the facet of an optical fiber, are the next step in development. This paper presents information on the analyses and modeling of an FPI using various numerical methods, namely the transfer matrix method (TMM), rigorous coupled-wave analysis (RCWA), and finite-difference time-domain (FDTD). It also covers a test facility for investigating issues related to the effect of temperature changes on the spectral range and phase shift. The results of temperature characterization were analyzed using methods devised during the simulation analyses. The results were subsequently compared to the simulated models to describe the underlying physical phenomena resulting in the observed spectral shifts.